1. Field of the Invention
The present invention generally relates to a biosensor and, more particularly, to a coupled waveguide-surface plasmon resonance biosensor using a grating and a metal material without labeling so as to detect bio-molecular interaction in real time.
2. Description of the Prior Art
In bio-molecular interaction analysis (BIA), bio-chips have attracted tremendous attention from genomics into proteomics. Bio-chips are used to detect genetic performance and bio-molecular messages. The current detection is done mainly by fluorescence detection. In fluorescence detection, problems related to complicated fluorescence tags, difficulty in molecule tags, inevitable fluorescence decay and unavailability in dynamics information of real-time interaction occur. Therefore, a label-free detecting method is required. In 1902, R. W. Wood discovered exceptional reflection gratings. Afterwards, theoretical reports and experiments on various grating structures such as guided-mode resonant sub-wavelength gratings were found in literature.
In United States Patent Application Doc. No. 20030068657, it is disclosed a label-free methods for performing assays using a colorimetric resonant reflectance optical biosensor. In this method, a grating is provided on a molecular detection platform for molecular implantation. Monochromatic light is generated after light passes the grating. A sample to be tested is disposed on the platform and is then illuminated by a white light beam. The wavelength of the incident light is changed after reflection because the molecules of the tested sample are bound to react with receptors on the grating. The change in wavelength can be detected by a spectrum analyzer so as to measure the thickness of the protein without using a probe for detecting fluorescence as well as radioactive tags. However, the reflectance spectrum exhibits a wide FWHM (full width at half magnitude) leading to a poor wavelength resolution so that detection in physiology concentration is unavailable.
Please refer to FIG. 1, which is a conventional waveguide-coupled biosensor disclosed in U.S. Pat. No. 6,483,096. In the biosensor 1 in FIG. 1, a sample 10 to be tested is provided on a grating structure G on a waveguide layer 11. The incident light 13 is coupled into the waveguide layer 11 by the grating structure G. The incoupled light 131 interacts with the substance , which emits fluorescent light 132 with a longer wavelength. The incoupled light 131 and the fluorescent light 132 are coupled out by the grating structure G such that the emitted outcoupled light 1311 is clearly separated from the exciting light 1321. Such a clear separation increases the signal-to-noise ratio of the sensor signal for molecular detection by using the tunable laser diode and the phase-locked loop (PLL) technique. However, the tunable laser diode provides a narrower range of wavelength and thus a high-precision goniometer is required so as to couple the incident light into the waveguide at a correct angle for resonance coupling.
Therefore, to overcome the aforementioned shortcomings, there is need in providing a high-precision waveguide-coupled biosensor so as to detect bio-molecular interaction in real time.